From aa0cdeb93cedef1e28bc3e4dc6cd4c5c3b1425d6 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Sat, 12 Oct 2024 15:00:24 +0200
Subject: [PATCH] [3.12] gh-125254: Fix error report about ambiguous option in
 argparse (GH-125273) (GH-125360)

This was a regression introduced in gh-58573. It was only tested for the
case when the ambiguous option is the last argument in the command line.
(cherry picked from commit 63cf4e914f879ee28a75c02e867baa7c6047ea2b)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
---
 Lib/argparse.py                                    |  2 +-
 Lib/test/test_argparse.py                          | 14 ++++++++++++--
 .../2024-10-10-19-57-35.gh-issue-125254.RtZxXS.rst |  1 +
 3 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-10-10-19-57-35.gh-issue-125254.RtZxXS.rst

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 2a3253453df..0e13ea5860d 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -2025,7 +2025,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
             if len(option_tuples) > 1:
                 options = ', '.join([option_string
                     for action, option_string, sep, explicit_arg in option_tuples])
-                args = {'option': arg_string, 'matches': options}
+                args = {'option': arg_strings[start_index], 'matches': options}
                 msg = _('ambiguous option: %(option)s could match %(matches)s')
                 raise ArgumentError(None, msg % args)
 
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 84f8b09fb1d..956c1cd505a 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -6310,9 +6310,19 @@ class TestExitOnError(TestCase):
     def test_ambiguous_option(self):
         self.parser.add_argument('--foobaz')
         self.parser.add_argument('--fooble', action='store_true')
+        self.parser.add_argument('--foogle')
         self.assertRaisesRegex(argparse.ArgumentError,
-                               "ambiguous option: --foob could match --foobaz, --fooble",
-                               self.parser.parse_args, ['--foob'])
+                "ambiguous option: --foob could match --foobaz, --fooble",
+            self.parser.parse_args, ['--foob'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                "ambiguous option: --foob=1 could match --foobaz, --fooble$",
+            self.parser.parse_args, ['--foob=1'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                "ambiguous option: --foob could match --foobaz, --fooble$",
+            self.parser.parse_args, ['--foob', '1', '--foogle', '2'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                "ambiguous option: --foob=1 could match --foobaz, --fooble$",
+            self.parser.parse_args, ['--foob=1', '--foogle', '2'])
 
     def test_os_error(self):
         self.parser.add_argument('file')
diff --git a/Misc/NEWS.d/next/Library/2024-10-10-19-57-35.gh-issue-125254.RtZxXS.rst b/Misc/NEWS.d/next/Library/2024-10-10-19-57-35.gh-issue-125254.RtZxXS.rst
new file mode 100644
index 00000000000..abe37fefedc
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-10-10-19-57-35.gh-issue-125254.RtZxXS.rst
@@ -0,0 +1 @@
+Fix a bug where ArgumentError includes the incorrect ambiguous option in :mod:`argparse`.